I don't see any thing wrong using But

but --> even though --> in contrary --> although are synonyms..(these are conjunctions used to introduce sub-ordinate clauses ) function quite similarly.

A is concise than D.
_________________

Between A and C is the toughest battle. So, I will explain my rational for that part.
PS: I am finding it extremely difficult to explain in words why such constructions are correct, but I will attempt anyways

e.g.
She nearly passed all her exams. (She passed none.)
She passed nearly all her exams. (She passed most of them.)
So, takeaway here is what does nearly modify?
In first case nearly modifies passed.
In second case nearly modifies all her exams.

So, using the same logic: (Lets say not as efficient is BAD, as efficient is GOOD)
In C: The author says: She is nearly BAD
In A: The author says: She is NOT nearly GOOD

Official Solution:

The new mayor is certainly more progressive than her predecessor, but she is not nearly as efficient.

A. but she is not nearly as efficient
B. but she, however, is not nearly as efficient
C. but she is nearly not as efficient
D. even though she is not nearly as efficient
E. despite being not as efficient


This sentence is correct and concise. She clearly refers to the new mayor, and the statement of her efficiency contains no unnecessary words.

1. The relationship between the subjects of clauses in this sentence is clear; the second clause is concise.
2. However is unnecessary.
3. Nearly is misplaced, making the clause awkward.
4. The phrase even though implies an incorrect logical relationship between the new mayor’s progressive stance and her efficiency.
5. Despite implies an incorrect logical relationship between the mayor’s progressive stance and her efficiency.

Answer: A
_________________